1. Field of the Invention
The present invention relates to door latches of the general type in which a slide bolt is retracted by turning a handle on either side of the door in either direction in opposition to a spring and the bolt is returned by the spring to an extended position. More particularly, the invention is directed to such door latches used on inside doors in an aircraft, as, for example, a lavatory door.
2. Description of the Prior Art
Latches on lavatory doors of a commercial airliner are not only subjected to heavy use, but to constant vibration while the plane is in operation. This vibration accentuates any play in the handles or other parts of the door latch and is likely to result in annoying rattling or chattering noises, particularly if the play is between two metal parts.
A typical door latch in commercial use on airliners is shown in U.S. Pat. No. 3,339,958. In that latch, the door handles interfit with the escutcheons and are tied together by a threaded square spindle having one or two nuts which, when tightened, force the handles to move along the spindle toward the escutcheon. Nylon spacers sleeved on the spindle serve as bushings for the spindle in the escutcheons and also as partial noise dampeners respecting chatter due to the axial play in the handles relative to the escutcheons, necessary if the handles are to be free turning. The problem is that the nuts cannot be tightened to an extent making the nylon spacers thrust members, for to do so would make the handles unduly difficult, if not impossible, to turn.
There has been a long felt need for a solution to the problem of rattle or looseness of play in door latches even before the difficulty became more acute in inside doors on commercial aircraft. For example, the problem was clearly spelled out in U.S. Pat. No. 2,242,866. In that patent, special toothed clutch faces were used for fine adjustment in backing off the handles from frictional engagement with the escutcheons.
Up to the time of the present invention, fine adjustment of the handle play and use of a dampening washer or the like have been the best approaches to the latch rattling problem. But component wear and other causes in time offset the finest of adjustments.